Visual perception is mediated by complex interactions amongst neurons in the retina, visual cortex and subcortical brain structures. The importance of vision to humans and other primates is reflected in the enormous percentage of cerebral cortex devoted to processing visual information. Thus, deficits in visual processing are particularly debilitating and arise from abnormalities not only in the eye, but also in cortical circuitry. For example, strabismus or amblyopia during childhood can have long-lasting effects on the cortical circuits that process visual information. There is also evidence that some forms of dyslexia result from central visual system abnormalities. The proposed studies are aimed at understanding the organization and function of neural circuits to and within the primary visual cortex (Vl), with the broader objective of contributing to understanding how neural circuits mediate the computations that underlie visual perception. In particular, these studies aim to identify: 1) the detailed functional organization of afferent input from the LGN to V1; 2) the functional connectivity between excitatory neurons and distinct types of inhibitory neurons in V1 and how these circuits relate to the functional organization of V1; 3) how the in vivo visual response properties of individual, identified neurons correlate with the connectivity of these same cell types, as revealed by our previous and ongoing in vitro studies. These goals will be achieved by: 1) directly recording visual responses from the terminal arbors of LGN afferents in V1, 2) using a combination of anatomical and physiological methods in living in vitro brain slice preparations; 3) recording visual responses of V1 neurons and labeling them with dye to correlate anatomically distinct cell types with function. In vitro brain slice studies will use scanning laser photostimulation to reveal the sources of local functional input to individual inhibitory neurons in V1. The same cells will be intracellularly labeled, stained with antibodies, and their intrinsic membrane properties assessed; the combined physiological and anatomical approach allows the identification of functional input sources to cells whose outputs and physiology are also characterized. The proposed studies will allow an unprecedented view of visual cortical circuits - they will reveal the detailed functional connectivity of neurons in visual cortex and how these circuits relate to the functional properties of the component neurons.